Hermetic compressor

ABSTRACT

A compression mechanism has a cylinder, a suction passage and a discharge passage. The suction passage of a cylinder is connected to a suction pipe. The discharge passage is open to an inner space of a sealed housing. A discharge gas is discharged through a discharge pipe. The cylinder is formed with a communicating passage extending from a suction passage to a suction pressure chamber to lead a suction gas in the suction passage into the suction pressure chamber and thereby allow a pressure of the suction gas in the suction passage to act on an outside surface of the cylinder.

TECHNICAL FIELD

This invention relates to a hermetic compressor in which a compressionmechanism and an electric motor are contained in a sealed housing, andparticularly relates to its structure in which the compression mechanismand the electric motor are resiliently supported in the sealed housing.

BACKGROUND ART

An example of known hermetic compressors of this type is one in which anelectric motor is integrally provided on top of a compression mechanismand a coil spring is interposed between the compression mechanism andthe inner surface of the bottom wall of a sealed housing to inhibit thetransmission of vibrations of the compression mechanism and the electricmotor to the sealed housing and thereby reduce the noise of thecompressor in operation (see, for example, Patent Document 1: JapaneseUnexamined Patent Publication No. H01-203688 (Pages 3 and 4 and FIG.1)).

In the above hermetic compressor in Patent Document 1, the upstream endof a suction passage is open at the sealed housing below the compressionmechanism and a suction pipe is connected to the opening of the suctionpassage to extend to the outside of the sealed housing. Gas led throughthe suction pipe into the sealed housing is sucked into a compressionchamber of the compression mechanism, compressed therein and thendischarged through a discharge port into the sealed housing. Thereafter,the discharge gas in the sealed housing is led to the outside through adischarge pipe connected to the sealed housing.

Problems to be Solved

As described above, the hermetic compressor in Patent Document 1 employsa structure that gas compressed in the compression mechanism isdischarged into the sealed housing. In this hermetic compressor, thesealed housing is filled with high-pressure discharge gas, so that thepressure of the discharge gas acts on the compression mechanism and theelectric motor placed inside the sealed housing. On the other hand,low-pressure suction gas is led through the suction passage into thecompression mechanism. In other words, the pressure of the suction gasacts on part of the compression mechanism in which the suction passageis formed. Therefore, a downward force acts on the compression mechanismowing to the difference between the discharge gas pressure and thesuction gas pressure, so that the compression mechanism and the electricmotor are pushed down.

If, like this, a downward force acts on the compression mechanism andthe electric motor, the coil spring supporting both these componentsmust bear both the gravity acting on the compression mechanism and theelectric motor and the force due to the gas pressure difference.Therefore, the coil spring should be hardened accordingly, which causesa problem that vibrations transmitted from the compression mechanism andthe electric motor to the sealed housing are increased.

Further, in order to prevent vibrations produced in the compressionmechanism and the electric motor from being transmitted to the sealedhousing, it is necessary to always keep the compression mechanism andthe electric motor away from contact with the sealed housing. Therefore,if the positions of the compression mechanism and the electric motor areshifted inside the sealed housing because of the difference between thedischarge gas pressure and the suction gas pressure as described before,this invites the need to ensure a larger clearance than necessarybetween the housing and the compression mechanism. As a result, aproblem arises that the sealed housing is upsized.

The present invention has been made in view of the above points and itsobject is to restrain that when the compression mechanism and theelectric motor are resiliently supported in the sealed housing, thepositions of the compression mechanism and the electric motor areshifted because of the difference between the discharge gas pressure andthe suction gas pressure, thereby achieving size reduction and noisereduction of the hermetic compressor.

DISCLOSURE OF THE INVENTION

To attain the above object, a first solution of the present invention isdirected to a so-called high-pressure dome type hermetic compressor inwhich a suction pipe is connected to a suction passage of a compressionmechanism while a discharge passage is communicated with the inner spaceof a sealed housing. Further, in the first solution, the suction gaspressure acts on the compression mechanism to reduce the pressing forceacting on the compression mechanism owing to discharge gas.

More specifically, a first aspect of the invention is directed to ahermetic compressor in which a compression mechanism (20) for suckinggas into a compression chamber (22) and compressing the gas therein andan electric motor (30) for driving the compression mechanism (20) arecontained in a sealed housing (10) and the compression mechanism (20) issupported, together with the electric motor (30), to the sealed housing(10) via a resilient member (65).

Further, the sealed housing (10) is connected to: a suction pipe (42)which leads suction gas into the hermetic compressor; and a dischargepipe (14) which leads discharge gas out of the hermetic compressor.Furthermore, the compression mechanism (20) is formed with: a suctionpassage (40) connected to the suction pipe (42) and open to thecompression chamber (22); and a discharge passage (41) communicated withthe inner space of the sealed housing (10) and open to the compressionchamber (22). In addition, the hermetic compressor further comprises adifferential pressure force canceling mechanism (52) for allowing thepressure of suction gas to act on the compression mechanism (20) so thatthe pressing force acting on the compression mechanism (20) along theaxis of the suction passage (40) owing to discharge gas in the sealedhousing (10) is reduced.

With the above structure, during operation of the hermetic compressor,the pressure of discharge gas in the sealed housing (10) acts on thecompression mechanism (20). Further, since the suction pipe (42) isconnected to the suction passage (40) of the compression mechanism (20),the pressure of suction gas led into the suction passage (40) also actson the compression mechanism (20). The differential pressure forcecanceling mechanism (52) allows the pressure of suction gas to furtheract on the compression mechanism (20) already acted on by the pressuresof discharge gas and suction gas. As a result, all the forces acting onthe compression mechanism (20), which are owing to the pressure ofdischarge gas in the sealed housing (10) and the pressure of suction gasled into the suction passage (40) and the pressure of suction gas actingthrough the differential pressure force canceling mechanism (52), arecanceled together. Therefore, the pressing force acting on thecompression mechanism (20) along the axis of the suction passage (40)can be reduced.

In the first aspect of the invention, the differential pressure forcecanceling mechanism (52) may be configured to be able to only reduce thepressing force acting on the compression mechanism (20) along the axisof the suction passage (40) or may be configured to be able to reduceand cancel out the pressing force.

In a second aspect of the invention, relating to the first aspect of theinvention, the compression mechanism (20) is formed of a rotary fluidmachine in which the compression chamber (22) is defined between theinner periphery of a cylinder (23) and the outer periphery of a piston(25). Further, the suction passage (40) in the compression mechanism(20) is formed to pass through the cylinder (23) in a radial directionof the cylinder (23). The differential pressure force cancelingmechanism (52) is configured to allow the pressure of suction gas to acton the outside surface of the cylinder (23) of the compression mechanism(20).

With the above structure, since the differential pressure forcecanceling mechanism (52) allows the suction gas pressure to act on theoutside surface of the cylinder (23), the pressing force acting on thecompression mechanism (20) along the axis of the suction passage (40)owing to discharge gas in the sealed housing (10), i.e., the pressingforce in the radial direction of the cylinder (23), can be reduced. Inthis manner, the differential pressure force canceling mechanism (52)allows the suction gas pressure to act directly on the cylinder (23) ofthe compression mechanism (20) in which the suction passage (40) isformed.

In a third aspect of the invention, relating to the second aspect of theinvention, the differential pressure force canceling mechanism (52) isconfigured to allow the pressure of suction gas to act on part of theoutside surface of the cylinder (23) opposite to the suction passage(40).

With the above configuration, the differential pressure force cancelingmechanism (52) allows the suction gas pressure to act on part of theoutside surface of the cylinder (23) opposite to the suction passage(40) passing through the cylinder (23). Thus, the position shift of thecompression mechanism (20) and electric motor (30) can be stablyrestrained even if the differential pressure force canceling mechanism(52) is configured to allow the suction gas pressure to act on a singlepoint on the cylinder (23).

In a fourth aspect of the invention, relating to the second aspect ofthe invention, the differential pressure force canceling mechanism (52)has a suction pressure chamber (50) defined between the inner surface ofthe sealed housing (10) and the outside surface of the cylinder (23) anda communicating passage (51) which communicates the suction pressurechamber (50) with the suction passage (40) of the compression mechanism(20) and is configured to allow the gas pressure in the suction pressurechamber (50) to act on the cylinder (23).

With the above structure, the suction gas pressure in the suctionpassage (40) is led through the communicating passage (51) to thesuction pressure chamber (50). The suction pressure chamber (50) isformed between the inner surface of the sealed housing (10) and theoutside surface of the cylinder (23). Then, the suction gas pressure ledto the suction pressure chamber (50) acts on the outside surface of thecylinder (23).

In a fifth aspect of the invention, relating to the fourth aspect of theinvention, the communicating passage (51) of the differential pressureforce canceling mechanism (52) is formed in the cylinder (23).

With the above structure, since the communicating passage (51) of thedifferential pressure force canceling mechanism (52) is formed in thecylinder (23) constituting part of the compression mechanism (20), thiseliminates the need to provide a separate member constituting thecommunicating passage (51).

In a sixth aspect of the invention, relating to the fourth aspect of theinvention, the communicating passage (51) of the differential pressureforce canceling mechanism (52) is formed in an arcuate shape thatextends along the inner periphery of the cylinder (23).

With the above structure, since the communicating passage (51) is formedbetween the outside surface and the inner periphery of the cylinder(23), heat transfer from the outside surface to inner periphery of thecylinder (23) can be inhibited by the communicating passage (51).Therefore, heat of high-temperature discharge gas in the sealed housing(10) becomes less likely to be transferred to the compression chamber(22).

In a seventh aspect of the invention, relating to the fourth aspect ofthe invention, the sealed housing (10) is connected to a plurality ofsuction pipes (42, 80), and one of the plurality of suction pipes (42,80) is connected to the suction passage (40) of the compressionmechanism (20) while the others are connected to the suction pressurechamber (50) of the differential pressure force canceling mechanism(52).

With the above structure, one suction pipe (42) of the plurality ofsuction pipes (42, 80) is communicated with the suction passage (40) andthe other suction pipe (80) is communicated via the suction pressurechamber (50) and the communicating passage (51) with the suction passage(40). Therefore, the suction gas is sucked through the plurality ofsuction pipes (42, 80) into the compression mechanism (20), whichreduces the flow rate of suction gas in each of the suction pipes (42,80).

A second solution of the present invention is directed to a so-calledlow-pressure dome type hermetic compressor in which a suction passage ofa compression mechanism is communicated with the inner space of a sealedhousing and a discharge passage is connected to a discharge pipe.Further, in the second solution, the discharge gas pressure acts on thecompression mechanism to cancel the force acting on the compressionmechanism owing to the discharge gas pressure.

More specifically, an eighth aspect of the invention is directed to ahermetic compressor in which a compression mechanism (20) for suckinggas into a compression chamber (22) and compressing the gas therein andan electric motor (30) for driving the compression mechanism (20) arecontained in a sealed housing (10) and the compression mechanism (20) issupported, together with the electric motor (30), to the sealed housing(10) via a resilient member (65).

Further, the sealed housing (10) is connected to: a suction pipe (42)which leads suction gas into the hermetic compressor; and a dischargepipe (14) which leads discharge gas out of the hermetic compressor.Furthermore, the compression mechanism (20) is formed with: a suctionpassage (40) communicated with the inner space of the sealed housing(10) and open to the compression chamber (22); and a discharge passage(41) connected to the discharge pipe (14) and open to the compressionchamber (22). In addition, the hermetic compressor further comprises adifferential pressure force canceling mechanism (52) for allowing thepressure of discharge gas discharged into the discharge pipe (14) to acton the compression mechanism (20) so that the force acting on thecompression mechanism (20) owing to the discharge gas is canceled.

With the above structure, during operation of the hermetic compressor,the pressure of suction gas in the sealed housing (10) acts on thecompression mechanism (20). Further, since discharge gas is led throughthe discharge passage (41) of the compression mechanism (20) into thedischarge pipe (14), the pressure of discharge gas discharged throughthe discharge passage (41) also acts on the compression mechanism (20).The differential pressure force canceling mechanism (52) allows thepressure of discharge gas to further act on the compression mechanism(20) already acted on by the pressure of discharge gas and the pressureof suction gas. As a result, the forces acting on the compressionmechanism (20), which are owing to the pressure of suction gas in thesealed housing (10), the pressure of discharge gas discharged throughthe discharge passage (41) and the pressure of discharge gas actingthrough the differential pressure force canceling mechanism (52), arecancelled together.

In the eighth aspect of the invention, the differential pressure forcecanceling mechanism (52) may be configured to be able to only reduce theforce acting on the compression mechanism (20) or may be configured tobe able to reduce and cancel out the force.

In a ninth aspect of the invention, relating to the eighth aspect of theinvention, the compression mechanism (20) is formed of a rotary fluidmachine in which the compression chamber (22) is defined between theinner periphery of a cylinder (23) and the outer periphery of a piston(25). Further, the discharge passage (41) in the compression mechanism(20) is open at the outside surface of the cylinder (23) and thedischarge pipe (14) is connected to an opening of the discharge passage(41) located at the outside surface of the cylinder (23). Thedifferential pressure force canceling mechanism (52) is configured toallow the pressure of discharge gas to act on the outside surface of thecylinder (23) of the compression mechanism (20).

With the above structure, since the differential pressure forcecanceling mechanism (52) allows the discharge gas pressure to act on theoutside surface of the cylinder (23), the force acting on thecompression mechanism (20) owing to discharge gas in the discharge pipe(14), i.e., the pressing force in the radial direction of the cylinder(23), can be reduced. In this manner, the differential pressure forcecanceling mechanism (52) allows the discharge gas pressure to actdirectly on the cylinder (23) of the compression mechanism (20) to whichthe discharge pipe (14) is connected.

In a tenth aspect of the invention, relating to the eighth aspect of theinvention, the compression mechanism (20) is formed of a rotary fluidmachine in which the compression chamber (22) is defined between theinner periphery of a cylinder (23) and the outer periphery of a piston(25). Further, out of a pair of end plate members (54, 55) that closethe end surfaces of the cylinder (23) of the compression mechanism (20),a first said end plate member (54) is passed through by the dischargepassage (41). Furthermore, the discharge pipe (14) is communicated withthe discharge passage (41). The differential pressure force cancelingmechanism (52) is configured to allow the pressure of discharge gas toact on a second said end plate member (55) of the compression mechanism(20).

With the above structure, the first end plate member (54) is formed withthe discharge passage (41) and the force toward the second end platemember (55) acts on the compression mechanism (20) owing to the pressureof discharge gas discharged through the discharge passage (41). On theother hand, the differential pressure force canceling mechanism (52)allows the discharge gas pressure to act on the second end plate member(55) opposed to the first end plate member (54) with the cylinder (23)interposed therebetween. Owing to the discharge gas pressure actingthrough the differential pressure force canceling mechanism (52), theforce toward the first end plate member (54) acts on the compressionmechanism (20). As a result, the force acting on the compressionmechanism (20) owing to the pressure of discharge gas discharged throughthe discharge passage (41) is cancelled out with the force acting on thecompression mechanism (20) through the differential pressure forcecanceling mechanism (52).

Effects of the Invention

In the first aspect of the invention, the hermetic compressor isprovided with the differential pressure force canceling mechanism (52)to reduce the pressing force acting on the compression mechanism (20)along the axis of the suction passage (40) owing to discharge gas in thesealed housing (10). This restrains the position shift of thecompression mechanism (20) and electric motor (30) owing to thedifference between the discharge gas pressure and suction gas pressurein the sealed housing (10). Since the position shift of the compressionmechanism (20) and electric motor (30) can be thus restrained, thehardness of the resilient member (65) can be set at such a value asrequired to bear only the gravity acting on the compression mechanism(20) and the electric motor (30). As a result, the compression mechanism(20) and the electric motor (30) are flexibly supported so thatvibrations can be inhibited from being transmitted from the compressionmechanism (20) and electric motor (30) to the sealed housing (10).Therefore, the noise of the hermetic compressor can be reduced.

Further, since the position shift of the compression mechanism (20) andelectric motor (30) can be restrained in the above manner, thiseliminates the need to ensure larger clearance than necessary betweenthe sealed housing (10) and both of the compression mechanism (20) andthe electric motor (30). Therefore, the sealed housing (10) can bedownsized and in turn the hermetic compressor can be downsized.

In the second aspect of the invention, the suction passage (40) radiallypassing through the cylinder (23) is formed in the compression mechanism(20) formed of a rotary fluid machine and the differential pressureforce canceling mechanism (52) allows the suction gas pressure to act onthe outside surface of the cylinder (23). Therefore, the suction gaspressure acts directly on the cylinder (23) formed with the suctionpassage (40), which restrains the position shift of the compressionmechanism (20) and electric motor (30) with ease and stability.

In the third aspect of the invention, the differential pressure forcecanceling mechanism (52) allows the suction gas pressure to act on partof the outside surface of the cylinder (23) opposite to the suctionpassage (40). Therefore, even if, for example, the differential pressureforce canceling mechanism (52) is configured to allow the suction gaspressure to act on a single point on the cylinder (23), it can stablyrestrain the position shift of the compression mechanism (20) andelectric motor (30). This simplifies the structure of the differentialpressure force canceling mechanism (52) and thereby reduces the cost ofthe hermetic compressor.

In the fourth aspect of the invention, the differential pressure forcecanceling mechanism (52) is formed with the suction pressure chamber(50) and the communicating passage (51) and is configured to allow thesuction gas pressure led into the suction pressure chamber (50) to acton the cylinder (23). Therefore, the differential pressure forcecanceling mechanism (52) can be achieved with a relatively simplestructure, which restrains the hermetic compressor from increasing incost for the reason of provision of the differential pressure forcecanceling mechanism (52).

In the fifth aspect of the invention, since the communicating passage(51) of the differential pressure force canceling mechanism (52) isformed in the cylinder (23), this eliminate the need to provide aseparate member constituting the communicating passage (51). Thisrestrains the number of parts from increasing for the reason ofprovision of the differential pressure force canceling mechanism (52)and avoids the upsizing of the hermetic compressor.

In the sixth aspect of the invention, the communicating passage (51)formed in the cylinder (23) is used to make it difficult to transferheat of high-temperature discharge gas in the sealed housing (10) to thecompression chamber (22). This reduces the amount of heat transferredfrom the discharge gas in the sealed housing (10) to the suction gas inthe compression chamber (22), thereby enhancing the efficiency ofcompression work.

In the seventh aspect of the invention, since the plurality of suctionpipes (42) are connected to the sealed housing (10) using the suctionpressure chamber (50) of the differential pressure force cancelingmechanism (52), the flow rate of suction gas in each of the suctionpipes (42) can be decreased so that the pressure loss of suction gasuntil it is sucked in the compression mechanism (20) can be reduced.This restrains the pressure drop of suction gas flowing into thecompression chamber (22) and thereby enhances the efficiency of thecompression mechanism (20).

In the eighth aspect of the invention, the hermetic compressor isprovided with the differential pressure force canceling mechanism (52)to cancel out the force of discharge gas discharged into the dischargepipe (14) on the compression mechanism (20). Therefore, the compressionmechanism (20) and the electric motor (30) can be restrained fromshifting their positions. This, like the first aspect of the invention,reduces the noise of the hermetic compressor and downsizes the hermeticcompressor.

In the ninth aspect of the invention, the discharge pipe (14) isconnected to the opening of the discharge passage (41) in the cylinder(23) of the compression mechanism (20) formed of a rotary fluid machineand the differential pressure force canceling mechanism (52) allows thedischarge gas pressure to act on the outside surface of the cylinder(23). Therefore, the discharge gas pressure acts directly on thecylinder (23) connected to the discharge pipe (14), which restrains theposition shift of the compression mechanism (20) and electric motor (30)with ease and stability.

In the tenth aspect of the invention, since the differential pressureforce canceling mechanism (52) allows the discharge gas pressure to acton the second end plate member (55) opposed to the first end platemember (54) formed with the discharge passage (41), the position shiftof the compression mechanism (20) and electric motor (30) can berestrained with ease and stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section showing a schematic structure ofa hermetic compressor according to an embodiment of the presentinvention.

FIG. 2 is a cross section taken along the line A-A of FIG. 1.

FIG. 3 is a corresponding view of FIG. 1 according to a variant.

FIG. 4 is a corresponding view of FIG. 2 according to the variant.

FIG. 5 is a corresponding view of FIG. 1 according to anotherembodiment.

FIG. 6 is a corresponding view of FIG. 1 according to a variant of saidanother embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the drawings.

FIG. 1 shows an embodiment of the present invention applied to aso-called “rocking piston type” rotary compressor (1). This compressoris configured to compress refrigerant during a cooling cycle in an airconditioner. In this compressor (1), a sealed housing (10) contains acompression mechanism (20) and an electric motor (30) which areconnected to each other through a drive shaft (31). The electric motor(30) is placed above and joined integrally to the compression mechanism(20). The compression mechanism (20) is resiliently supported to thesealed housing (10) via mounting mechanisms (63).

The sealed housing (10) is formed in a size that a predeterminedclearance is left between the sealed housing (10) and both of thecompression mechanism (20) and the electric motor (30) so that thecompression mechanism (20) and electric motor (30) in operation cannotbe made contact with the inner surface of the sealed housing (10).Further, the sealed housing (10) has a vertically elongated barrel (11),a saucer-shaped upper end plate (12) fitted into the upper end of thebarrel (11), and a lower end plate (13) placed at the bottom of thebarrel (11) and having a larger diameter than the outside diameter ofthe barrel (11). The barrel (11), the upper end plate (12) and the lowerend plate (13) are bonded together by welding the upper and lower endsof the barrel (11) all around to the upper end plate (12) and the lowerend plate (13), respectively.

The upper end plate (12) is provided substantially at the center with adischarge pipe (14) vertically penetrating the upper end plate (12).Further, a terminal (16) for supplying electricity to the electric motor(30) is disposed in part of the upper end plate (12) radially away fromthe discharge pipe (14).

The sealed housing (10) is equipped with two block members (43, 46).Each block member (43, 46) is formed in a relatively short column.Further, the head surface of each block member (43, 46) is rounded atthe entire circumference. Out of the two block members (43, 46), thefirst block member (43) is formed with a through hole (43 a). Thethrough hole (43 a) is formed coaxially with the first block member (43)and open at the head and bottom surfaces of the first block member (43).One end of a suction pipe (42) is inserted in the through hole (43 a) ofthe first block member (43). On the other hand, the remaining secondblock member (46) is solid.

The block members (43, 46) are attached to the barrel (11).Specifically, two insertion holes (11 a, 11 b) for inserting the blockmembers (43, 46) therein are formed in opposed positions, one by one, inparts of the barrel (11) slightly lower than its vertical middle. Thehead of the first block member (43) is inserted in one insertion hole(11 a), while the head of the second block member (46) is inserted inthe other insertion hole (11 b). In this state, each block member (43,46) is welded to the barrel (11). In other words, the block members (43,46) are disposed, one by one, on the same level of the barrel (11) and180 degrees circumferentially away from each other, so that the headsurfaces of the block members (43, 46) are opposed to each other.Further, the head surfaces of the block members (43, 36) inserted in thebarrel (11) form parts of the inner surface of the sealed housing (10).

The compression mechanism (20) includes a cylinder (23) formed in asubstantially cylindrical shape. On top of the cylinder (23), a fronthead (54) is placed as a first end plate member for closing an openingof the cylinder (23) located in the top surface thereof. On the otherhand, on the bottom of the cylinder (23), a rear head (55) is placed asa second end plate member for closing another opening of the cylinder(23) located in the bottom surface thereof. The front head (54) and therear head (55) are joined integrally to the cylinder (23) by fasteningusing bolts or the like (not shown). The compression mechanism (20) ispositioned so that the center line of the cylinder (23) substantiallycoincides with the center line of the barrel (11).

A rocking piston (25) is inserted in the cylinder (23) to rock with therotation of the drive shaft (31). Further, in the cylinder (23), acompression chamber (22) is defined by the outer periphery of therocking piston (25), the inner periphery of the cylinder (23), thebottom surface of the front head (54) and the top surface of the rearhead (55).

As shown in FIG. 2, the rocking piston (25) is constructed so that anannular body (25 a) is formed integrally with a flat blade (25 b)extending radially outward from a point on the outer periphery of thebody (25 a). The body (25 a) is formed so that during its rockingmovement, its outer periphery comes substantially in line contact withthe inner periphery of the cylinder (23). Further, the blade (25 b) isinserted in and supported to an insertion hole (28) formed in part ofthe cylinder (23) located outwardly of the compression chamber (22), soas to be sandwiched between a pair of bushes (27) in the insertion hole(28). The blade (25 b) divides the compression chamber (22) intolow-pressure and high-pressure sides.

The cylinder (23) is formed with a suction passage (40). One end of thesuction passage (40) is open at part of the inner periphery of thecylinder (23) adjoining the low-pressure side of the compression chamber(22). The suction passage (40) extends linearly from the one endradially outward along the center line of the cylinder (23). The distalend of the suction passage (40) is open at the outside surface of thecylinder (23). Further, the cylinder (23) is formed with two dischargepassages (41) just beside the bush (27). The discharge passages (41) areformed in pair so that one is bored from the top surface of the cylinder(23) and the other is bored from the bottom surface thereof.

The cylinder (23) is also formed with a communicating passage (51). Thecommunicating passage (51) is constituted by an arcuate section (51 a)and a linear section (51 b). The arcuate section (51 a) extendssubstantially semi-circularly along the half of the inner periphery ofthe cylinder (23) adjoining the low-pressure side of the compressionchamber (22). The root end of the arcuate section (15 a) is connected tothe suction passage (40), while the distal end thereof is located at aposition in the cylinder (23) opposite to the suction passage (40). Onthe other hand, the linear section (51 b) of the communicating passage(51) extends linearly from the distal end of the arcuate section (51 a)radially outward of the cylinder (23). The linear section (51 b) isformed so that its central axis is located on the central axis of thesuction passage (40). Further, the distal end of the linear section (51b) of the communicating passage (51) is open at the outside surface ofthe cylinder (23).

The front head (54) and the rear head (55) are formed with head'sdischarge passages (56, 57) communicating with the discharge passages(41), respectively, located in the cylinder (23). The top surface of thefront head (54) and the bottom surface of the rear head (55) areprovided with discharge valves (48) for opening/closing the head'sdischarge passages (56, 57), respectively. The discharge valves (48) areeach composed of a lead valve. The head's discharge passages (56, 57)are communicated with the inner space of the sealed housing (10) whenthe discharge valves (48) are opened. Therefore, this compressor (1) isconstructed as a so-called high-pressure dome type compressor in whichthe suction passage (40) of the compression mechanism (20) is connectedto the suction pipe (42) and the discharge passages (56, 57) thereof arecommunicated with the inner space of the sealed housing (10).

The front head (54) is formed at the center with an upwardly extendingcylindrical part (58). The cylindrical part (58) constitutes a slidingbearing for supporting the drive shaft (31). A substantially disc-shapedupper muffler (59) is fixed to the front head (54) to cover the head'sdischarge passage (56) from above. On the other hand, the rear head (55)is also formed at the center with a downwardly extending cylindricalpart (60). The cylindrical part (60) also constitutes a sliding bearingfor supporting the drive shaft (31). A substantially disc-shaped lowermuffler (61) is fixed to the rear head (55) to cover the head'sdischarge passage (57) from below. The lower muffler (61) acts toprevent refrigeration oil in the lower part of the barrel (11) fromflowing into the discharge passages (41, 57) of the cylinder (23).

The lower muffler (61) is formed of a thicker plate material than theupper muffler (59). A plurality of mounting mechanisms (63) are disposedon the outer periphery of the bottom surface of the lower muffler (61)at circumferentially spaced intervals. Each mounting mechanism (63) iscomposed of a mount (64) fixed to the lower end plate (13), a coilspring (65) as a resilient member anchored to the top of the mount (64)to extend upward from the mount (64) and anchored at its upper end tothe underside of the lower muffler (61), and a stopper (66) forrestricting the compression of the coil spring (65). In this manner, thelower muffler (61) also acts as a bracket through which the compressionmechanism (20) is mounted on the coil springs (65).

The compression mechanism (20) is positioned substantially on the samelevel as the first and second block members (43, 46) attached to thesealed housing (10). Further, the compression mechanism (20) is placedso that the opening of the suction passage (40) in the outside surfaceof the cylinder (20) faces the first block member (43) and the openingof the communicating passage (51) in the outside surface of the cylinder(23) faces the second block member (46).

The part of the outside surface of the cylinder (23) at which thesuction passage (40) is open extends slightly outward in the radialdirection of the cylinder (23). The end surface of the above slightlyextending part forms a flat surface, at which the suction passage (40)is open. The flat end surface at which the suction passage (40) is openfaces the head surface of the first block member (43), which is alsoflat. A relatively narrow clearance is left between these two flatsurfaces. Further, the cylinder (23) is formed with an annular groove(23 a) to surround the opening of the suction passage (40) in the endsurface of the above extending part. The annular groove (23 a) is formedby digging the outside surface of the cylinder (23) all around theopening of the suction passage (40). The annular groove (23 a) is formedwith a larger diameter than the opening edge of the suction passage(40).

An O-ring (45) is fitted in the annular groove (23 a). The O-ring (45)is formed with a larger diameter than the opening of the suction passage(40) of the cylinder (23) and the through hole (43 a) of the first blockmember (43). The size of the O-ring (45) is selected so that it can bebrought into tight contact with both the bottom surface of the annulargroove (23 a) of the cylinder (23) and the head surface of the firstblock member (43) and can be squashed between the cylinder (23) and thefirst block member (43). Further, the O-ring (45) is kept in tightcontact with both the cylinder (23) and the first block member (43) evenif the compression mechanism (20) shifts its position during operation.

Further, since the outer periphery of the O-ring (45) faces the innerspace of the sealed housing (10), the pressure of the discharge gas inthe inner space of the sealed housing (10) acts on the outer peripheryof the O-ring (45). Therefore, the O-ring (45) receives a force to tendto deform it in the direction to reduce its diameter. Since, however,the inner periphery of the O-ring (45) is held on the side surface ofthe annular groove (23 a) toward the opening of the suction passage(40), this prevents the O-ring (45) from deforming in the direction toreduce its diameter.

In this manner, the O-ring (45) seals the clearance between the cylinder(23) and the first block member (43) to ensure air-tightness through thesuction gas passage from the suction pipe (42) to the suction passage(40).

The part of the outside surface of the cylinder (23) at which the linearsection (51 b) of the communicating passage (51) is open extendsslightly outward in the radial direction of the cylinder (23). The endsurface of the above slightly extending part forms a flat surface, atwhich the communicating passage (51) is open. The flat end surface atwhich the communicating passage (51) is open faces the head surface ofthe second block member (46), which is also flat. A relatively narrowclearance is left between these two flat surfaces. Further, the cylinder(23) is formed with an annular groove (23 a) to surround the opening ofthe communicating passage (51) in the end surface of the above extendingpart. The annular groove (23 a) is formed by digging the outside surfaceof the cylinder (23) all around the opening of the communicating passage(51). The annular groove (23 a) is formed with a larger diameter thanthe opening edge of the communicating passage (51).

An O-ring (47) is fitted in the annular groove (23 a). The O-ring (47)is formed with a larger diameter than the opening of the linear section(51 b) of the communicating passage (51) and has the same diameter asthe O-ring (45) provided at the suction passage (40) side of thecylinder (23). The size of the O-ring (47) is selected so that it can bebrought into tight contact with both the bottom surface of the annulargroove (23 a) of the cylinder (23) and the head surface of the secondblock member (46) and can be squashed between the cylinder (23) and thesecond block member (46). Further, the O-ring (47) is kept in tightcontact with both the cylinder (23) and the second block member (46)even if the compression mechanism (20) shifts its position duringoperation.

Further, since the outer periphery of the O-ring (47) faces the innerspace of the sealed housing (10), the pressure of the discharge gas inthe inner space of the sealed housing (10) acts on the outer peripheryof the O-ring (47). Therefore, the O-ring (47) receives a force to tendto deform it in the direction to reduce its diameter. Since, however,the inner periphery of the O-ring (47) is held on the side surface ofthe annular groove (23 a) toward the opening of the communicatingpassage (51), this prevents the O-ring (47) from deforming in thedirection to reduce its diameter.

In the clearance between the cylinder (23) and the second block member(46), its portion located within the O-ring (47) forms a suctionpressure chamber (50) separated from the surrounding parts. The suctionpressure chamber (50) is divided from the inner space of the sealedhousing (10) filled with discharge gas and communicates with the suctionpassage (49) via the communicating passage (51). Further, theair-tightness of the suction pressure chamber (50) is held by the O-ringis (47) in tight contact with the cylinder (23) and the second blockmember (46). The suction pressure chamber (50) and the communicatingpassage (51) constitute a differential pressure force cancelingmechanism (52).

A brushless DC motor is used as the electric motor (30). The electricmotor (30) is composed of a cylindrical stator (32) fixed to the fronthead (54) of the compression mechanism (20), and a rotor (33) placedrotatably in the stator (32). The drive shaft (31) is inserted and fixedinto a center hole (33 a) of the rotor (33).

The drive shaft (31) is positioned so that its center line substantiallycoincides with the center line of the cylinder (23). The lower portionof the drive shaft (31) is formed with an eccentric part (31 a). Theeccentric part (31 a) is formed with a larger diameter than the otherparts of the drive shaft (31) and its center line is eccentric withrespect to the axis of the drive shaft (31). Further, the drive shaft(31) passes through the body (25 a) of the rocking piston (25) placed inthe cylinder (23) so that the outer periphery of the eccentric part (31a) can slide on the inner periphery of the body (25 a).

The rim of the stator (32) has a plurality of circumferentially spacedprojections (32 a) extending to the proximity of the lower end of theupper end plate (12). Parts of the stator (32) just below theprojections (32 a) are formed with vertically penetrating through holes(32 b), respectively. On the other hand, the top of the front head (54)of the compression mechanism (20) is formed with bosses (54 a)associated with the through holes (32 b) of the stator (32). The stator(32) is fixed integrally to the front head (54) by inserting bolts (67)into the through holes (32 b) and screwing them into the bosses (54 a),respectively.

The projections (32 a) of the stator (32) are provided for the purposeof preventing an excessive position shift of the compression mechanism(20) and electric motor (30). For example, when a large excitation forceis applied to the compression mechanism (20) and the electric motor (30)because of vibrations during transportation of the compressor (1), theprojections (32 a) abut on the lower end of the upper end plate (12) tothereby prevent an excessive position shift of the compression mechanism(20) and electric motor (30).

In the compressor (1) having the above structure, when the electricmotor (30) is activated to rock the rocking piston (25), suction gas ledthrough the suction pipe (42) into the compressor (1) is sucked into thecompression chamber (22) through the suction passage (40). The suctiongas sucked in the compression chamber (22) is compressed by the rockingpiston (25). Then, the compressed gas passes through the dischargepassage (41) in the cylinder (23) and the head's discharge passages (56,57) in this order. The pressure of the discharge gas at this time causesthe discharge valves (48) to open so that the compressed gas refrigerantin the compression chamber (22) is discharged as discharge gas into thesealed housing (10). The inner space of the sealed housing (10) isfilled with discharge gas from the compression mechanism (20) andthereby put under high pressure. Thereafter, the discharge gas is ledthrough the discharge pipe (14) to the outside of the sealed housing(10).

Effects of Embodiment

During operation of the above compressor (1), vibrations of the electricmotor (30) occur and vibrations of the compression mechanism (20) occurowing to torque variations caused by its compression work. Since in theabove compressor (1) the compression mechanism (20) and the electricmotor (30) are mounted on the coil springs (65), vibrations generated bythe compression mechanism (20) and the electric motor (30) are absorbedto some extent by the coil springs (65). This reduces vibrationstransmitted from the compression mechanism (20) and the electric motor(30) to the sealed housing (10).

Further, since in the above compressor (1) the O-ring (45) is interposedbetween the outside surface of the cylinder (23) and the first blockmember (43), vibrations transmitted from the cylinder (23) to thesuction pipe (42) can be restrained. Therefore, according to thisembodiment, the noise of the compressor (1) can be reduced.

Furthermore, since the above compressor (1) is constructed as ahigh-pressure dome type one, the high pressure of the discharge gas inthe sealed housing (10) acts uniformly on the entire compressionmechanism (20) and the entire electric motor (30). On the other hand,low-pressure suction gas is led through the suction pipe (42) into thesuction passage (40) of the cylinder (23) of the compression mechanism(20). Therefore, the pressure of suction gas acts on a region of thecompressor (1) within the O-ring (45) located toward the suction passage(40). Further, the compressor (1) is provided with the differentialpressure force canceling mechanism (52) and the pressure of suction gasin the suction passage (40) is led into the suction pressure chamber(50) through the communicating passage (51). Therefore, the pressure ofsuction gas also acts on a region of the cylinder (23) within the O-ring(47) located opposite to the suction passage (40).

To sum up, while the pressure of discharge gas in the sealed housing(10) acts on the entire compression mechanism (20), pressures of suctiongas in opposite directions act on equal-area regions of the cylinder(23) of the compression mechanism (20) toward and opposite to thesuction passage (40). Thus, all the forces acting on the compressionmechanism (20) owing to the discharge gas pressure and suction gaspressure on the compression mechanism (20) are cancelled out, whichreduces the pressing force acting on the compression mechanism (20)along the axis of the suction passage (40) to substantially zero.

Since, therefore, the force due to the difference between the dischargegas pressure and the suction gas pressure does not act on thecompression mechanism (20), the spring constant of the coil springs (65)can be set at a value as small as required to bear only the gravityacting on the compression mechanism (20) and the electric motor (30).Hence, the spring constant of the coil springs (65) can be softened.This further makes it difficult to transmit vibrations of thecompression mechanism (20) and the electric motor (30) to the housingand thereby reduces the noise of the compressor (1) well.

Further, since the pressing force acting on the compression mechanism(20) along the axis of the suction passage (40) is reduced by thedifferential pressure force canceling mechanism (52) as described above,the position shift of the compression mechanism (20) and the electricmotor (30) can be restrained. As a result, the clearance between thecompression mechanism (20) and the inner surface of the sealed housing(10) can be reduced. Therefore, the sealed housing (10) can be formedwith a smaller size by the amount of reduction of the clearance, whichpermits downsizing of the compressor (1).

Further, the above embodiment is configured so that the suction gaspressure acts on part of the outside surface of the cylinder (23)opposite to the suction passage (40). Specifically, the differentialpressure force canceling mechanism (52) is configured to allow thesuction gas pressure to act on a single point on the outside surface ofthe cylinder (23). This stably reduces the pressing force along the axisof the suction passage (40). Therefore, the structure of thedifferential pressure force canceling mechanism (52) can be simplified,which reduces the cost of the compressor (1). Furthermore, since thedifferential pressure force canceling mechanism (52) allows the suctiongas pressure to act directly on the outside surface of the cylinder(23), the position shift of the compression mechanism (20) and theelectric motor (30) can be restrained with ease and stability.

In the above embodiment, the suction pressure chamber (50) is formedbetween the head surface of the second block member (46) and the outsidesurface of the cylinder (23) so that the pressure of suction gas ledthrough the communicating passage (51) acts on the outside surface ofthe cylinder (23). Therefore, the differential pressure force cancelingmechanism (52) can be achieved with a relatively simple structure, whichrestrains the compressor (1) from increasing in cost for the reason ofprovision of the differential pressure force canceling mechanism (52).Further, if the part of the outside surface of the cylinder (23) formingthe suction pressure chamber (50) is changed in area, the force on thecylinder (23) can be also changed which is created by the differentialpressure force canceling mechanism (52).

Since the communicating passage (51) of the differential pressure forcecanceling mechanism (52) is formed in the cylinder (23), a separatemember forming the communicating passage (51) can be dispensed with.This prevents the number of parts from increasing for the reason ofprovision of the differential pressure force canceling mechanism (52)and avoids upsizing of the compressor (1).

Since the communicating passage (51) is formed to extend along thelow-pressure side inner periphery of the compression chamber (22) of thecylinder (23), a space is created between the outside surface of thecylinder (23) and the compression chamber (22). Thus, the communicatingpassage (51) inhibits heat transfer from the outside surface to innerperiphery of the cylinder (23). As a result, heat of high-temperaturedischarge gas discharged into the sealed housing (10) becomes lesslikely to be transferred to the compression chamber (22). This restrainsheating of suction gas sucked in the compression chamber (22) andthereby enhances the efficiency of compression work.

The above embodiment is configured so that the differential pressureforce canceling mechanism (52) allows the suction gas pressure to act ona single point on the cylinder (23). The present invention is notlimited to the above configuration but may be configured so that, thoughnot shown, the suction gas pressure acts on plural points on thecylinder (23). Specifically, if the differential pressure forcecanceling mechanism (52) allows the suction gas pressure to act on twopoints on the outside surface of the cylinder (23), suction pressurechambers of the same configuration as in the above embodiment are formedat substantially regular intervals, i.e., at intervals of 120°, alongthe circumference of the cylinder (23) with respect to the formationpoint of the suction passage (40) in the cylinder (23). Further, thecylinder (23) is formed with a plurality of communicating passages whichcommunicates the suction passage (40) with each of the suction pressurechambers.

Likewise, if the differential pressure canceling mechanism (52) allowsthe suction gas pressure to act on three points on the outside surfaceof the cylinder (23), suction pressure chambers are formed at intervalsof 90°. If, like these cases, the suction gas pressure acts on theoutside of the cylinder (23) at substantially regular intervals, thepressing force acting on the compression mechanism (20) can be stablyreduced.

Though a single suction pipe (42) is disposed in the above embodiment,two suction pipes can be disposed as in a variant shown in FIGS. 3 and4. In this case, the second block member (46) is configured to have thesame configuration as the first block member (43) and one end of asuction pipe (80) similar to the suction pipe (42) is inserted into thethrough hole of the second block member (46). Since the suction pipe(80) communicates with the suction passage (40) via the communicatingpassage (51), suction gas is sucked into the compression chamber (22)through the two suction pipes (42, 80). As a result, the flow rate ofsuction gas in each of the suction pipes (42, 80) is decreased. Thisreduces the pressure loss of suction gas until it is sucked into thecompression chamber (22), thereby enhancing the efficiency of thecompression mechanism (20). If two or more suction pressure chambers areprovided, the number of suction pipes is increased accordingly.

Another Embodiment

The present invention is not limited to the above embodiment butincludes various other embodiments. The above embodiment is describedfor the case where the present invention is applied to a high-pressuredome type hermetic compressor. The present invention is not limited tothe above case but may be applied to another embodiment as shown in FIG.5, i.e., a low-pressure dome type hermetic compressor (1) in which asuction passage (not shown) of a compression mechanism (20) iscommunicated with the inner space of a sealed housing (10) and adischarge passage (41) of the compression mechanism (20) is connected toa discharge pipe (14). Below, this embodiment will be described onlyabout different points from the above embodiment while the same partsare identified by the same reference numerals.

In this embodiment, the suction passage and the discharge passage (41)are disposed in an opposite side of the cylinder (23) to those in theabove embodiment. The discharge passage (41) passes through the fronthead (54). The downstream end opening of the discharge passage (41)adjoins a discharge space (82) defined by the top surface of the fronthead (54) and the upper muffler (59). The discharge space (82) iscommunicated with a connecting passage (83), which downwardly passesthrough the front head (54) and extends in the cylinder (23). Thedownstream end of the connecting passage (83) is open at the outsidesurface of the cylinder (23) and the opening at the downstream endthereof is connected to the upstream end of the discharge pipe (14).

The discharge pipe (14) extends from its upstream end downward along oneside of the compression mechanism (20), extends radially past below thecompression mechanism (20) to the opposite side thereof and then extendsupward along the inner periphery of the barrel (11). The upper part ofthe discharge pipe (14) is formed spirally so that vibrations of thecompression mechanism (20) and electric motor (30) in operation can beabsorbed. The downstream end part of the discharge pipe (14), i.e., theupper end part thereof, extends out through the center of the upper endplate (12) and is fixed to the upper end plate (12).

The discharge pipe (14) is provided with a branch pipe (85). The branchpipe (85) allows the discharge gas pressure to act on part of theoutside surface of the cylinder (23) located opposite to part thereofwhere the connecting passage (83) is formed, so that the pressure ofdischarge gas discharged into the discharge pipe (14) cancels the forceacting on the compression mechanism (20). Thus, the branch pipe (85)constitutes a differential pressure force canceling mechanism (52) inthe present invention. Since in this embodiment the discharge passage(41) is not open at the bottom surface of the cylinder (23) andtherefore no lower muffler is provided, the bottom surface of the rearhead (55) of the compression mechanism (20) is resiliently supported tothe lower end plate (13) via the mounting mechanisms (63).

In this embodiment, during operation of the compressor (1), the suctiongas pressure in the sealed housing (10) acts uniformly on the entirecompression mechanism (20) and the entire electric motor (30). Further,since the discharge pipe (14) is connected to the connecting passage(83) of the cylinder (23) of the compression mechanism (20) so thatdischarge gas is discharged into the discharge pipe (14), the pressureof discharge gas acts on the cylinder (23). Furthermore, the branch pipe(85) constituting the differential pressure force canceling mechanism(52) allows the pressure of discharge gas in the discharge pipe (14) toact on the part of the cylinder (23) opposite to the part thereof atwhich the discharge pipe (14) is connected to the cylinder (23).

To sum up, while the pressure of suction gas in the sealed housing (10)acts on the entire compression mechanism (20), pressures of dischargegas in opposite directions act on the part of the cylinder (23) of thecompression mechanism (20) where the discharge pipe (14) is connectedand the opposite part of the cylinder (23). Thus, all the forces actingon the compression mechanism (20) owing to the suction gas pressure anddischarge gas pressure on the compression mechanism (20) are cancelled,which reduces the force acting on the compression mechanism (20).

As a result, like the above embodiment, the noise of the compressor (1)can be reduced well and the compressor (1) can be downsized. Further,since the discharge gas pressure acts directly on the cylinder (23) towhich the discharge pipe (14) is connected, the position shift of thecompression mechanism (20) and electric motor (30) can be restrainedwith ease and stability.

In this embodiment, as a variant shown in FIG. 6, the discharge pipe(14) may be placed so that its upstream end part penetrates the uppermuffler (59) and the discharge pipe (14) may be communicated with thedischarge passage (41) via the discharge space (82). In this case, abranch pipe (85) branched from the discharge pipe (14) allows thedischarge gas pressure to act on part of the bottom surface of the rearhead (55) located below part of the compression mechanism (20) locatedjust below the discharge pipe (14), so that the discharge gas cancelsthe force acting on the compression mechanism (20).

Also in this variant, since the force acting on the compressionmechanism (20) is reduced by the difference between the discharge gaspressure and the suction gas pressure, this reduces the noise of thecompressor (1) well and downsizes the compressor (1). Further, thedifferential pressure force canceling mechanism (52) allows thedischarge gas pressure to act on the rear head (55) opposed to the fronthead (54) formed with the discharge passage (41). In this case, theforce due to discharge gas discharged into the discharge pipe (14) andthe force due to the differential pressure force canceling mechanism(52) act on the compression mechanism (20) in vertically oppositedirections. Therefore, the position shift of the compression mechanism(20) and electric motor (30) can be restrained with ease and stability.

The above embodiments are described for the case where the presentinvention is applied to a rocking piston type rotary compressor (1) inwhich the piston (25) is formed integrally with the blade (25 b) so thatthe piston (25) can rock in the cylinder (23). The compressor to whichthe present invention is applicable is not limited to the above type.For example, the present invention is applicable to a rolling pistontype rotary compressor in which a piston is provided separately from ablade and the distal end of the blade is pressed against the outerperiphery of the piston.

INDUSTRIAL APPLICABILITY

As seen from the above, the hermetic compressor according to the presentinvention is useful when a compression mechanism and an electric motorare contained in a sealed housing and particularly suitable when thecompression mechanism and the electric motor are resiliently supportedin the sealed housing.

1. A hermetic compressor comprising: a sealed housing connected to asuction pipe that leads a suction gas into the sealed housing and adischarge pipe that leads a discharge gas out of the sealed housing; acompression mechanism disposed in the sealed housing, and including acompression chamber, a suction passage connected to the suction pipe andopen to the compression chamber, and a discharge passage fluidlyconnected to an inner space of the sealed housing, and open to thecompression chamber; an electric motor disposed in the sealed housing torotate about a rotation axis, the electric motor being operativelycoupled to the compression mechanism; a differential pressure forcecanceling mechanism configured to allow a pressure of the suction gas toact on the compression mechanism to reduce a pressing force from thedischarge gas in the sealed housing that acts on the compressionmechanism along an axis of the suction passage, the differentialpressure force cancelling mechanism forming a space with pressure of thesuction gas between the sealed housing and the compression mechanism;and a resilient member supporting the compression mechanism and theelectric motor relative to the sealed housing along the rotation axis,an open end of the suction pipe having an end face that faces anexternal surface of the compression mechanism having an opening of thesuction passage formed therein, with a sliding connection fluidlyconnecting the open end of the suction pipe and the opening of thesuction passage such that an area between the open end of the suctionpipe and the opening of the suction passage is sealed and such that theopening of the suction passageway is movable along the rotation axisrelative to the open end of the suction pipe.
 2. The hermetic compressorof claim 1, wherein the compression mechanism is formed of a rotaryfluid machine having a cylinder and a piston, the compression chamber isdefined between an inner periphery of the cylinder and an outerperiphery of the piston, the suction passage is formed to pass throughthe cylinder in a radial direction of the cylinder, and the differentialpressure force canceling mechanism is configured to allow the pressureof the suction gas to act on an outside surface of the cylinder.
 3. Thehermetic compressor of claim 2, wherein the differential pressure forcecanceling mechanism is configured to allow the pressure of the suctiongas to act on a portion of the outside surface of the cylinder oppositethe suction passage.
 4. The hermetic compressor of claim 2, wherein thedifferential pressure force canceling mechanism has a suction pressurechamber defined between an inner surface of the sealed housing and theoutside surface of the cylinder and a communicating passage that fluidlyconnects the suction pressure chamber with the suction passage, thecommunicating passage is configured to allow a gas pressure in thesuction pressure chamber to act on the cylinder.
 5. The hermeticcompressor of claim 4, wherein the communicating passage of thedifferential pressure force canceling mechanism is formed in thecylinder.
 6. The hermetic compressor of claim 4, wherein thecommunicating passage of the differential pressure force cancelingmechanism is formed in a substantially arcuate shape that extends alongthe inner periphery of the cylinder.
 7. The hermetic compressor of claim4, wherein the sealed housing connected to a plurality of suction pipes,and one of the suction pipes is connected to the suction passage of thecompression mechanism while the other is connected to the suctionpressure chamber of the differential pressure force canceling mechanism.8. The hermetic compressor of claim 1, wherein the sealed housing has anopening with block member mounted therein, and the space with pressureof the suction gas is formed between the block member and thecompression mechanism.
 9. The hermetic compressor of claim 8, whereinthe block member is solid in order to block the hole in the sealedhousing from fluid communication therethrough.
 10. The hermeticcompressor of claim 8, wherein the block member has a through holeconfigured to receive an additional suction pipe.